Newsweek's Anne Underwood files this report on Wii Fit:

As a health writer, I know the awesome benefits of exercise--improving cardiac and lung function, encouraging weight loss, boosting strength and endurance, improving mood and possibly even making you smarter. In theory, that's all terrific. It's the bit about getting to the gym more than twice a week that's the problem. Now Nintendo's new Wii Fit is bringing the gym--or a stripped-down version of it--to me and my Mii (the Wii's onscreen representation of me). At $90--plus $250 for the basic console--Wii Fit is not cheap, but it still costs less than an actual gym membership. And since it's in the middle of my living room, it's harder to ignore. That can only be good news.

Wii Fit follows on the success of the original Wii console, which has been a coveted item since its November 2006 release. Reaching well beyond the teenage-male fan base of the standard videogame, the basic Wii has attracted kids, soccer moms and seniors. Certain rehab centers are using it to help patients recover from strokes, injuries and, in some cases, war wounds. Physical therapists have even come up with a name for this new form of rehab--"Wiihab."

Where the original Wii featured golf, boxing, tennis, baseball and bowling, Wii Fit offers fitness training of four types--aerobics, strength training, yoga and balance games. Most of the exercises are fun, and all of them increase your heart rate or muscle tone while helping develop "core" muscle groups that aid balance and posture.

The key to all of this is the Wii Fit balance board that you stand on. It looks like a glorified kitchen cutting board but contains weight-sensitive areas for both feet. The concept came from a Nintendo developer who saw sumo wrestlers on TV weighing themselves with two scales. (Japanese scales go up to only about 300 pounds, so two scales are often necessary.) While trying out the two-scale idea, "developers noticed that keeping the balance between your left and right legs is actually very challenging and fun," says Cammie Dunaway, executive vice president of sales and marketing for Nintendo of America. Developers recruited Kaoru Matsui, a Japanese trainer, who was already using balance concepts, to advise them on specific exercises.

Don't even think about trying to fool the board. It uses four sensors to measure your body weight 60 times a second. It gauges not only the total pressure on each foot but also how your weight is distributed. It notes your tiniest wobbles and translates this into eerie insight into your posture and balance. On the ski jump, you have to position yourself just right, in alignment with a dot on the screen, as your Mii barrels down the slope. Then, as you reach the bottom of the ski jump, you straighten your knees, rise onto your toes and hold the pose to lift off and sail through the air. If you're successful, you'll enjoy waving to the applause of a virtual crowd. (If you're not, expect to tumble head over heels in an avalanche of snow and skis that's not pretty. Fall off the tightrope in the exercise of the same name, and it doesn't show us what happens.) At the end of each of the 40-plus exercises, you receive not only a numeric score but also a one-to-four star rating, from "unbalanced" at one end of the spectrum to "yoga master," "bodybuilder" or "calorie incinerator" at the other.

At their best, gadgets like Wii Fit can help people get in shape by combining exercise with the addictiveness of videogames. A half hour on the elliptical can be boring. Not so a videogame that's always offering you new rewards, like vocal encouragement ("great job") and extra points in the Wii Bank that unlock new exercises. Studies have shown that earlier games like Dance Dance Revolution helped people lose weight by making them want to come back for more. Can the Wii Fit hold one's interest for the months needed to lose weight and get in shape? Perhaps. But it certainly tries to ensnare your competitive spirit, allowing you to monitor your progress and play against family members. And there is the ever-present challenge of meeting your weight-loss goals, which the scale-based system excels in tracking.

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